Dual torsion bar chair control

ABSTRACT

A tiltable platform is tiltably mounted to a stationary platform and its tilting movement is controlled by a dual torsion bar mechanism between the two platforms. The leg of one generally Ushaped torsion bar is received in a pocket in the stationary platform and the corresponding leg of another generally U-shaped torsion bar is received in a like pocket in the tiltable platform. The base portions of the torsion bars project generally parallel to the tilt axis, away from these pockets. The opposite legs of the torsion bars are received in a channel-shaped interconnecting bracket which includes an adjusting mechanism to adjust the pretension on the bars.

llnited States Patent 1191 Mohr et al.

[ May 28, 1.974

[ DUAL TORSION BAR CHAIR CONTROL [751 Inventors: Robert G. Mohr, Grand Rapids;

Adrian R. Olree, Caledonia, both of Mich.

[73] Assignee: Steelcase 1nc., Grand Rapids, Mich.

[221 Filed: Apr. 21, 1972 21 1 Appl. No.: 246,381

3,740,014 6/1973 Swenson et al. 248/373 Primary Examiner-Marion Parsons, Jr.

& Cooper [57] ABSTRACT A tiltable platform is tiltably mounted to a stationary platform and its tilting movement is controlled by a dual torsion bar mechanism between the two platforms. The leg of one generally U-shaped torsion bar is received in a pocket in the stationary platform and the corresponding leg of another generally U-shaped torsion bar is received in a like pocket in the tiltable platform. The base portions of the torsion bars project generally parallel to the tilt axis, away from these pockets. The opposite legs of the torsion bars are received in a channel-shaped interconnecting bracket which includes an adjusting mechanism to adjust the pretension on the bars.

24 Claims, 3 Drawing (Figures i DUAL TORSION BAR CHAIR CONTROL BACKGROUND OF THE INVENTION tionary platform supported by the base and a tiltable I platform tiltably mounted on the stationary platform.

In particular, this invention relates to torsion bartype chair controls. Conventionally, such controls include a torsion bar of generally square cross section having one end fixed against rotation in a square aperture in the stationary platform. The other end of the bar is rotatably carried in a rotatable bushing at the opposite side of the stationary platform. A lever is fixed against rotation with respect to the rotatable end of the torsion bar and is operably connected to the tiltable member such that tilting of the tiltable member rotates the rotatable end of the torsion bar and generates a torsion force.

One drawback to such mechanisms is that they have to be quite long in order to accommodate a torsion bar having a sufficiently flat rate of change curve. Consequently, they are bulky to the eye and are fairly readily apparent when one looks at the chair.

This problem can be minimized by utilizing a dual torsion bar mechanism in which one end of a rod of generally square cross section is fixed in a square aperture in the stationary member and the corresponding end of a similarly square bar is fixed against rotation in a square aperture in the tiltable platform. The free end of the first bar is rotatably carried in a rotatable bushing in the opposite side of the stationary platform and the free end of the second torsion bar is rotatably carried in a similar bushing in the opposite side of the tiltable platform. The two bars are then interconnected at their rotatable ends by some means which will transmit the rotation motion of one bar to the other bar.

This does result in a control mechanism which is more compact, since it can be about half the length. However, such a mechanism is somewhat more expensive to construct since it requires two separate bars, two separate sets of rotatable bushings, increases assembly costs because of the necessity of assembling the bars into the bushings and into the apertures, andetc. Accordingly, such a mechanism has not been the entire answer to the problem.

SUMMARY OF THE PRESENT INVENTION The present invention constitutes a dual torsion bar chair control which is both less expensive to construct and which is actually more compact in construction than prior art dual torsion bar mechanisms.

Compactness is achieved by providing two generally U-shaped torsion bars, each having a first leg, a second leg and a base. The first leg of each bar is received in a pocket in each of the tiltable and stationary members, respectively. The bases of the torsion bars extend from the pockets generally parallel to the axis about which the tiltable member tilts. The second legs extend inwardly towards one another and are joined by an interconnecting means which transmits the rotation of one of the bars to the other. The base portions of the torsion bars provide the torsional spring action, while the leg portions provide resilient bending in series therewith. While such resilient bending is not essentialto two torsion bars to be even shorter than the torsion bars used in previous dual torsion bar mechanisms.

Turning to the economy with which this invention can be constructed, such economy is achieved by the elimination of the need for any rotatable bushings at the rotatable ends of the torsion means, the elimination of the need to place apertures in the respective stationary and tiltable members at the rotatable ends of the torsion bars, and the elimination of the need to assemble the rotatable ends of the torsion bars and the bushings into such apertures. This is achieved by mounting the rotatable ends of the torsion bars directly in the interconnecting means which transmits the rotation of one bar to the other. The interconnecting means itself is then free of connection with either the tiltable member or the stationary member. Thus, the assembly of the interconnecting means to the two torsion bars completes the assembly of the chair control.

The fact that the bars are generally U-shaped, having bent legs at either end further facilitates economy. First, it makes the assembly of the interconnecting means more economical, since it eliminates the need for mounting any kind of levers on the torsion means for joining to the interconnecting means. Secondly, it makes it possible to use a bar of generally circular cross section, rather than a bar of square cross section. This is because the first legs are received in pockets at one side of the stationary and tiltable members, respectively, and because there is no need to mount any kind of levers on the torsion bars. A torsion bar of circular cross section is not only less expensive, but also improves stress distribution in the bar. Indeed, this further contributes to the compactness of the control, since the better distribution of forces makes it possible to use a torsion bar of lesser cross-sectional area. This in turn results in a flatter spring curve and makes it possible to use even shorter torsion bars.

In another aspect of the invention, compactness is achieved by providing a torsion means operably connected to the stationary member and to the tiltable member and a resilient bending means operably connected in series with the torsion means, between the tiltable and stationary members, whereby a flatter springcurve can be obtained with a more compact torsion means. Actually, this aspect of the invention can be used in connection even with a single torsion rod chair control as well as with a dual torsion rod chair control.

These and other aspects and objects of the invention will be further understood and appreciated by reference to the written specification and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded, perspective view of the chair control;

FIG. 2 is a plan view of the assembled chair control;

FIG. 3 is a cross-sectional view taken along plane III- --llI of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, the tilting of tiltable platform 30 with respect to stationary platform 10 is controlled by a front generally U-shaped torsion bar 50 and a rear generally U-shaped torsion bar 60 (FIGS. 1 and 2). One leg 51 of front bar 50 is mounted in a pocket 20 of stationary platform while the corresponding leg 61 of rear bar 60 is received in pocket 38 of tiltable platform 30. The opposite legs 52 and 62 of front torsion bar 50 and rear torsion bar 60, respectively, are received in an interconnecting bracket 70 which transmits the rotation of one bar to the other. Bracket 70 is free-floating with respect to tiltable platform 30 and stationary platform 10, i.e., it is free of connection to either. Adjustment assembly 80 in interconnecting bracket 70 provides a means for adjusting the pretension in front torsion bar 50 and rear torsion bar 60.

Stationary platform 10 is constructed of metal by casting, stamping or the like. It is generally pan-shaped, having a front wall 11, sidewalls 12 and bottom 13. An inverted, generally cup-shaped spindle mount 14 is secured to bottom 13 by welding or the like. The top of a spindle 15 then projects upwardly through an aperture in bottom 13 and through an aperture in spindle mount 14 and is fixedly secured to stationary platform 10 at these points.

Stationary platform 10 includes an aperture 19 in each sidewall 12 thereof whereby tiltable platform 30 can be tiltably mounted thereto. To limit the extent to which tiltable platform 30 can be tilted forwardly, a front stop 16 is mounted on the top edge of front wall 11. It is made of a sound-deadening material or cushioning material. To limit the extent to which platform 30 can be tilted rearwardly, a rear stop 17, of a sounddeadening or cushioning material, is mounted on a raised portion 13a of bottom wall 13 at a rear corner of stationary platform 10.

To facilitate mounting of front torsion bar 50, a small curved flange is welded to the left sidewall 12 (as viewed in FIG. 1) of stationary member 10 to thereby define a receiving pocket 20. Pocket 20 receives the left leg (as viewed in FIG. 1) 51 of front bar 50 and is shaped to confine leg 51 against rotational movement. In this manner, the left end of front torsion bar 50 is fixed against rotation with respect to stationary platform 10. Near the opposite side of stationary platform 10, a torsion bar bearing 18 is secured both to bottom 13 and to front wall 11. Torsion bar bearing 18 is made of a sound-deadening or cushioning material and acts as a stop to prevent front torsion bar 50 from noisily clinking against the bottom 13 of stationary platform 10. By so controlling front torsion bar 50, it also controls rear torsion bar 60 and interconnecting bracket 70 in a similar manner.

Finally, stationary platform 10 includes an aperture 21 in the bottom 13 thereof at the right-hand side thereof as viewed in FIG. 1. When the control is finally assembled, adjustment assembly 80 of interconnecting bracket 70 is positioned generally above aperture 21, and aperture 21 thereby provides access to adjustment assembly 80.

Tiltable platform is also constructed of metal by casting, stamping or the like. It is generally frame-- shaped, including a front wall 31, sidewalls 32 and rear wall 33. At the top of sidewalls 32 and rear wall 33 is a seat mounting flange 34 including apertures 39 therein to facilitate mounting a seat thereto. At the top of front wall 31, there is a front stop flange 35 which projects rearwardly a short distance from front wall 31. Front stop flange 35 cooperates with front stop 16 on stationary platform 10. The lower rear surface 38a of pocket 38 cooperates in a similar way with rear stop 17 on stationary platform 10.

- The sidewalls 32 of tiltable platform 30 include apertures 37 therein to facilitate mounting tiltable platform 30 to stationary platform 10. To achieve this mounting, apertures 37 are aligned with apertures 19 and a bearing 40 is inserted through both apertures. A washer 42 is slipped over the end of the bearing and a rivet 41 is inserted into the end of the bearing to thereby hold the bearing in place.

Tiltable platform 30 also includes a flange welded to the left side 32 thereof to define a pocket 38. Pocket 38 is similar in construction and function to pocket 20 on stationary platform 10. It receives the left end 61 of rear torsion bar 60 and confines it in such a way that rear torsion bar 60is fixed at its left end against rotation with respect to tiltable platform 30.

In order to provide access to adjustment assembly 80 when the control is finally assembled, the entire bottom of tiltable platform 30 is completely open. This not only leaves room for access through aperture 21 to adjustment assembly 80, but also makes the assembly of tiltable platform 30 to stationary platform 10 much easier by allowing tiltable member 30 to be slipped over the top of stationary member 10.

Each of the two torsion bars and is generally U-shaped in configuration. Front bar 50 includes a leg 51, a leg 52 and a base 53. Similarly, rear bar 60 includes a leg 61, a leg 62 and a base 63. Both bars are generally circular in cross section. Finally, the leg 52 of front bar 50 includes a groove 54 at the very end thereof to facilitate its cooperation with adjustment assembly 80 (FIG. 3). Leg 62 of rear bar 60 includes a similar groove 64, also for facilitating cooperation with adjustment assembly 80.

Interconnecting bracket is generally channelshaped, having a pair of sidewalls 71 and a bottom 72. (FIGS. 1 and 3). Bottom 72 slopes downwardly from the ends of bracket 70 toward the center thereof. In operatiomthe ends 74 of bottom wall 72 define fulcrum points upon which the legs 52 and 62 of the torsion bars rest. The bottom -72 slopes away from these fulcrum points in order to allow legs 52 and 62 room to be twisted by adjustment assembly 80. Finally, bottom 72 includes an aperture 73 at the center thereof to facilitate mounting adjustment assembly thereto. Adjustment assembly 80 includes a nut 82 threadably mounted on a bolt 81. The head 81 rests against the underside of bottom 72 and the threaded portion or stem of bolt 81 extends through aperture 73 (FIG. 3). Preferably, the head of bolt 81 is adapted to receive an allen wrench for purposes of adjusting the pretension on front bar 50 and rear bar 60. Nut 82 is generally T- shaped, having a crossbar 83. The ends of crossbar 83 overlie the upper surfaces of legs 52 and 62 to thereby hold them in place against fulcrum points 74. Preferably, crossbar 83 includes a downwardly depending hook 84 at each end thereof for mating engagement with grooves 54 and 64, respectively, of legs 52 and 62.

In assembly, tiltable platform 30 is tiltably mounted to stationary platform 10 by means of bearings 40 through aligned apertures 37 and 19. Tiltable platform 30 is merely slipped over the top of stationary platform 10 until apertures 37 and 19 are aligned. Bearings 40 are then inserted and held in place in the manner heretofore described. it will be noted that the left side 12 of stationary platform ll) includes a cutaway portion 12a at its rear corner in order to accommodate pocket 38 of tiltable platform 30. Front torsion bar 50 is mounted with its leg 51 in pocket 20 of stationary platform while rear torsion bar 60 is mounted with its leg 61 in pocket 38 of tiltable member 30. The base portions 53 and 63 then extend from pockets and 38, respectively, generally parallel to the axis about which tiltable member tilts. The opposite legs 52 and 62 of the torsion bars extend inwardly towards one another and are embraced between the channel sidewalls 71 of interconnecting bracket 70. Nut 82 of adjustment assembly 80 overlies the upper surfaces of legs 52 and 62 and thereby holds them against fulcrum points 74 of interconnecting bracket 70. The torsion bars are further held in place by the downwardly depending hooks 84 of nut 82 being matingly received in grooves 54 and 64, respectively, of legs 52 and 62.

OPERATION In operation, a chair, or a chair back alone, is operably connected to tiltable platform 30 in a conventional fashion. When the particular chair member is tilted, the tiltable platform 30 tilts about bearings with respect to stationary platform 10. Since the left leg 51 is fixed against rotation with respect to stationary member 10, and since the left leg 61 of rear torsion bar 60 is fixed against rotation with respect to tiltable member 30, and since the right legs 52 and 62 of the bars are interconnected by interconnecting bracket 70, both bars will begin to twist and thereby set up a torsional resistance to tilting of tiltable member 30. The presence of torsion bar bearing 18 at the front right end of stationary member 10 prevents front torsion bar from deflecting downwardly and clinking against the metal bottom 13 of stationary platform 10. Because of this restraining action, interconnecting bracket 70 and rear torsion bar are similarly prevented from deflecting downwardly and creating such a clinking noise.

In addition to the twisting motion which is set up in front torsion bar 50 and rear torsion bar 60, a bending action is created in legs 51, 52, and 62. Such bending is in series with the torsional rotation of the base portions 53 and 63 of the torsion rods. This gives the overall torsion bar assembly a flatter spring curve, and enables one to use shorter torsion bars.

Because torsion bars 50 and 60 can be mounted through the use of their legs, the torsion bars can be of generally circular cross section, instead of generally square cross section as is conventional for such torsion bars. This results in better force distribution and makes it possible to use torsion bars of generally less crosssectional area. Because they have generally less crosssectional area, the torsion bars are not as stiff, and have a flatter spring curve. They can be made even shorter as a result of this factor.

In order to effect adjustment of a pretension on the torsion bars 50 and 60, an allen wrench can be used to thread bolt 81 further into or out of nut 82 in order to apply a greater or lesser twist on the bars 50 and 60. The head of bolt 81 is readily accessible through the open bottom of tiltable platform 30 and through the aperture 21 in stationary platform l0.

As a result of these features, the present invention comprises a chair control which can be both more com pact than conventional chair controls and which is less expensive to construct than previous dual torsion rod chair controls. Of course, it is understood that the above is merely a preferred embodiment of the invention, and that many changes and alterations can be made thereof without departing from its spirit or broader aspects.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a chair control having a tiltable member tiltably mounted to a stationary member, a first torsion bar operably connected at a first end to said tiltable member, said first end being fixed against rotation with respect thereto, a second torsion bar operably connected at a first end to said stationary member, said first end being fixed against rotation with respect thereto, and means interconnecting said first and second bars at a point spaced from said first ends thereof for transmitting the rotation of one of said bars to the other, the improvement comprising: said torsion bars having their second ends mounted in said interconnecting means, said interconnecting means being free of connection with said tiltable member and said stationary member.

2. The chair control of claim 1 in which each of said bars is generally U-shaped in configuration, including first and second legs and a base; a pocket in each of said tiltable and stationary members respectively for receiving said first legs of said first and second torsion bars respectively; said interconnecting means operably connecting said second legs of said torsion bars.

3. The chair control of claim 2 in which said torsion bars are generally circular in cross section.

4. The chair control of claim 3 in which said interconnecting means comprises a generally channelshaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending upwardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars.

5. The chair control of claim 4 in which said adjustment means comprises a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs.

6. The chair control of claim 5 in which said crossbar includes a downwardly projecting hook at each end thereof; each of said second legs including a recess in the top surface thereof for matingly receiving said hooks.

7. In a chair control having a tiltable member tiltably mounted to a stationary member, the improvement comprising: a torsion rod operably connected to said stationary member and to said tiltable member for generating torque therebetween, about the longitudinal axis of said torsion rod, when said tiltable member is tilted; a resilient bending means operably connected in series with said torsion rod, between said tiltable member and said stationary member, said bending means being sufficiently bendable relative to the torque generated in said torsion rod that a flatter spring curve can be obtained with a more compact torsion rod.

8. In a chair control having a tiltable member tiltably mounted to a stationary member, the improvement comprising: a torsion means operably connected to said stationary member and to said tiltable member for generating torque therebetween when said tiltable member is tilted; a resilient bending means operably connected in series with said torsion means, between said tiltable member and said stationary member, whereby a flatter spring curve can be obtained with a more compact torsion means; said torsion means and said resilient bending means both comprising a torsion rod having at least one bend therein; one end of said torsion bar being fixed against rotation with respect to said stationary member; said torsion bar extending from said one end generally parallel to the axis about which said tiltable member tilts; said torsion bar including a leg extending from said bend in a direction generally perpendicular to said axis of tilting; means operably connecting said leg to said tiltable member whereby said tilting bends said leg and simultaneously twists that portion of said torsion bar which is parallel to said tilting axis; said leg having a substantial length relative to the length of said bar from said one end to said bend whereby said bending of said leg is sufficient relative to said twisting of said bar to give said chair control a flatter spring curve with a more compact torsion bar.

9. The chair control of claim 8 in which said operable connecting means comprises a firstmeans engaging the upper surface of the end of said leg and a second means engaging the under surface of said leg at a point closely adjacent said bend whereby said leg tends to bend between said first engaging means and said second engaging means.

10. The chair control of claim 9 in which two such torsion bars are provided, the first of said torsion bars having one end fixed against rotation with respect to said stationary member and the second having one end fixed against rotation with respect to said tiltable member; each of said torsion bars including said bend and said leg; said operable connecting means comprising a means interconnecting both said legs whereby the rotation of one of said rods is transmitted to the other.

11. In a chair control having a tiltable member tiltably mounted on a stationary member, a first torsion means operably connected at a first end to said tiltable member, said first end being fixed against rotational movement with respect to said tiltable member, a second torsion means operably connected at a first end to said stationary member, said first end being fixed against rotation with respect, to said stationary memher, and means interconnecting said first and second torsion means at a point spaced from said fixed ends thereof for transmitting the rotation of one to the other, the improvement comprising: at least one of said first and second torsion means being capable of resilient bending movement as wellas torsional movement; at least one of said first and second torsion means being free to bend with respect to said stationary and tiltable members, and said interconnecting means being sufficiently rigid that tilting of said tiltable member results in bending of said one torsion means as well as simultaneously twisting of both said torsion means.

12. The chair control of claim 11 in which both of said torsion bars are free to bend with respect to said stationary and tiltable members.

13. The chair control of claim 12 in which each of said bars is generally U-shaped in configuration, including first and second legs and a base; a pocket in each of said tiltable and stationary members respectively for receiving said first legs of said first and second torsion bars respectively; said interconnecting means operably connecting said second legs of said torsion bars.

14. The chair control of claim 13 in which said torsion bars are generally circular in cross section.

15. The chair control of claim 14 in which said interconnecting means comprises a generally channelshaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending up wardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second'legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars; said adjustment means comprising a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs; said crossbar including a downwardly projecting hook at each end thereof; each of said second legs including a recess in the top surface thereof for matingly receiving said hooks.

16. In a chair control having a tiltable member tiltably mounted to a stationary member, and first and second torsion bars, the improvement comprising: each of said first and second torsion bars being generally U- shaped, having a first leg, a second leg and a base; means in said stationary member for fixedly receiving said first leg of said first torsion bar and means in said tiltable member for fixedly receiving said first leg of said second torsion bar; said bases of said torsion bars extending from said receiving means generally parallel to the axis about which said tiltable member tilts; said second legs of said first and second torsion bars extending inwardly towards one another; interconnecting means embracing said second legs for transmitting the rotation of one of said bars to the other.

17. The chair control of claim 16 in which said interconnecting means is free of any fixed connection with said stationary and tiltable members.

18. The chair of claim 16 in which each said receiving means comprises a pocket embracing said first leg.

19. The chair control of claim 18 in which said torsion bars are generally circular in cross section.

20. The chair control of claim 16 in which said torsion bars are generally circular in cross section.

21. The chair control of claim 20 in which said interconnecting means comprises a generally channelshaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending upwardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars; said adjustment means comprising a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs.

22. The chair control of claim 21 in which said stasecond legs at a point near its juncture with said base. a: 

1. In a chair control having a tiltable member tiltably mounted to a stationary member, a first torsion bar operably connected at a first end to said tiltable member, said first end being fixed against rotation with respect thereto, a second torsion bar operably connected at a first end to said stationary member, said first end being fixed against rotation with respect thereto, and means interconnecting said first and second bars at a point spaced from said first ends thereof for transmitting the rotation of one of said bars to the other, the improvement comprising: said torsion bars having their second ends mounted in said interconnecting means, said interconnecting means being free of connection with said tiltable member and said stationary member.
 2. The chair control of claim 1 in which each of said bars is generally U-shaped in configuration, including first and second legs and a base; a pocket in each of said tiltable and stationary members respectively for receiving said first legs of said first and second torsion bars respectively; said interconnecting means operably connecting said second legs of said torsion bars.
 3. The chair control of claim 2 in which said torsion bars are generally circular in cross section.
 4. The chair control of claim 3 in which said intErconnecting means comprises a generally channel-shaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending upwardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars.
 5. The chair control of claim 4 in which said adjustment means comprises a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs.
 6. The chair control of claim 5 in which said crossbar includes a downwardly projecting hook at each end thereof; each of said second legs including a recess in the top surface thereof for matingly receiving said hooks.
 7. In a chair control having a tiltable member tiltably mounted to a stationary member, the improvement comprising: a torsion rod operably connected to said stationary member and to said tiltable member for generating torque therebetween, about the longitudinal axis of said torsion rod, when said tiltable member is tilted; a resilient bending means operably connected in series with said torsion rod, between said tiltable member and said stationary member, said bending means being sufficiently bendable relative to the torque generated in said torsion rod that a flatter spring curve can be obtained with a more compact torsion rod.
 8. In a chair control having a tiltable member tiltably mounted to a stationary member, the improvement comprising: a torsion means operably connected to said stationary member and to said tiltable member for generating torque therebetween when said tiltable member is tilted; a resilient bending means operably connected in series with said torsion means, between said tiltable member and said stationary member, whereby a flatter spring curve can be obtained with a more compact torsion means; said torsion means and said resilient bending means both comprising a torsion rod having at least one bend therein; one end of said torsion bar being fixed against rotation with respect to said stationary member; said torsion bar extending from said one end generally parallel to the axis about which said tiltable member tilts; said torsion bar including a leg extending from said bend in a direction generally perpendicular to said axis of tilting; means operably connecting said leg to said tiltable member whereby said tilting bends said leg and simultaneously twists that portion of said torsion bar which is parallel to said tilting axis; said leg having a substantial length relative to the length of said bar from said one end to said bend whereby said bending of said leg is sufficient relative to said twisting of said bar to give said chair control a flatter spring curve with a more compact torsion bar.
 9. The chair control of claim 8 in which said operable connecting means comprises a first means engaging the upper surface of the end of said leg and a second means engaging the under surface of said leg at a point closely adjacent said bend whereby said leg tends to bend between said first engaging means and said second engaging means.
 10. The chair control of claim 9 in which two such torsion bars are provided, the first of said torsion bars having one end fixed against rotation with respect to said stationary member and the second having one end fixed against rotation with respect to said tiltable member; each of said torsion bars including said bend and said leg; said operable connecting means comprising a means interconnecting bOth said legs whereby the rotation of one of said rods is transmitted to the other.
 11. In a chair control having a tiltable member tiltably mounted on a stationary member, a first torsion means operably connected at a first end to said tiltable member, said first end being fixed against rotational movement with respect to said tiltable member, a second torsion means operably connected at a first end to said stationary member, said first end being fixed against rotation with respect, to said stationary member, and means interconnecting said first and second torsion means at a point spaced from said fixed ends thereof for transmitting the rotation of one to the other, the improvement comprising: at least one of said first and second torsion means being capable of resilient bending movement as well as torsional movement; at least one of said first and second torsion means being free to bend with respect to said stationary and tiltable members, and said interconnecting means being sufficiently rigid that tilting of said tiltable member results in bending of said one torsion means as well as simultaneously twisting of both said torsion means.
 12. The chair control of claim 11 in which both of said torsion bars are free to bend with respect to said stationary and tiltable members.
 13. The chair control of claim 12 in which each of said bars is generally U-shaped in configuration, including first and second legs and a base; a pocket in each of said tiltable and stationary members respectively for receiving said first legs of said first and second torsion bars respectively; said interconnecting means operably connecting said second legs of said torsion bars.
 14. The chair control of claim 13 in which said torsion bars are generally circular in cross section.
 15. The chair control of claim 14 in which said interconnecting means comprises a generally channel-shaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending upwardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars; said adjustment means comprising a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs; said crossbar including a downwardly projecting hook at each end thereof; each of said second legs including a recess in the top surface thereof for matingly receiving said hooks.
 16. In a chair control having a tiltable member tiltably mounted to a stationary member, and first and second torsion bars, the improvement comprising: each of said first and second torsion bars being generally U-shaped, having a first leg, a second leg and a base; means in said stationary member for fixedly receiving said first leg of said first torsion bar and means in said tiltable member for fixedly receiving said first leg of said second torsion bar; said bases of said torsion bars extending from said receiving means generally parallel to the axis about which said tiltable member tilts; said second legs of said first and second torsion bars extending inwardly towards one another; interconnecting means embracing said second legs for transmitting the rotation of one of said bars to the other.
 17. The chair control of claim 16 in which said interconnecting means is free of any fixed connection with said stationary and tiltable members.
 18. The chair of claim 16 in which each said receiving means comprises a pocket embrAcing said first leg.
 19. The chair control of claim 18 in which said torsion bars are generally circular in cross section.
 20. The chair control of claim 16 in which said torsion bars are generally circular in cross section.
 21. The chair control of claim 20 in which said interconnecting means comprises a generally channel-shaped bracket having sidewalls and a bottom; said sidewalls embracing said second legs of said torsion bars, each of said second legs extending inwardly towards the other, from an end of said channel-shaped bracket; each of said second legs contacting said bottom at a respective fulcrum point; said bottom sloping downwardly from said fulcrum point, towards the center of said bracket; an adjustment means extending upwardly from the center of said bottom, passing between the ends of said second legs, and overlying the tops of said second legs for holding said second legs against said fulcrum points and for facilitating the adjustment of pretension on said torsion bars; said adjustment means comprising a generally T-shaped nut, having a stem and a crossbar, threaded on a bolt; said bolt extending upwardly through an aperture in said bottom of said bracket; said crossbar of said nut overlying said second legs.
 22. The chair control of claim 21 in which said stationary and tiltable members include apertures in the bottom thereof; the head of said bolt being accessible through said apertures.
 23. The chair control of claim 22 in which said crossbar includes a downwardly projecting hook at each end thereof; each of said second legs including a recess in the top surfaces thereof for matingly receiving said hooks.
 24. The control of claim 16 in which said interconnecting means comprises: first means engaging the end of each said second leg on one surface thereof; second means engaging the opposite surface at each of said second legs at a point near its juncture with said base. 